The present invention relates to the field of satellite communications. More particularly, the present invention relates to a multi-feed antenna suitable for satellite communications.
Geostationary direct broadcast systems (DBS) are geostationary satellite systems that are direct competitors to terrestrially-based cable television systems. Such DBS systems have the advantage of allowing a terrestrially-based receiver to receive a plurality of television channels from virtually any location on Earth, while a cable television subscriber must be connected to a cable television system to receive television signals. Terrestrial-based cable television systems have the advantage over DBS systems of allowing a subscriber to have a high-bandwidth Internet connection through the cable television system, while such a connection is unavailable through a DBS system. Currently, digital links to the Internet are available through the fixed satellite system (FSS), another system of geostationary satellites.
U.S. Pat. No. 5,859,620 to Skinner et al. relates to a multiband feedhorn satellite receiving antenna that receives signals from more than 30 satellites that are longitudinally spaced in geosynchronous orbits above the equator of the Earth. According to Skinner et al., a satellite receiving antenna includes a torodial reflector having a circular cross-section in a horizontal (longitudinal or azimuthal) plane and a parabolic cross-section in an elevational plane. The size of the Skinner et al. reflector requires a plurality of braces for support and is far too large for use in a residential environment.
U.S. Pat. No. 5,805,116 to Morley discloses to an ultra-small aperture antenna for a satellite communications terminal having a dish reflector and separate transmit and receive feedhorns. According to Morley, a receive feedhorn is spatially offset from a transmit feedhorn. Both feedhorns are disposed within a focal point zone such that the receive feedhorn is positioned at an ideal focal point of the dish reflector. The transmit feedhorn is positioned to have an aperture offset from the ideal focal point, but is still within the focal point zone of the dish reflector. The receive feedhorn is disposed at the ideal focal point for maximizing gain of received signals. A disadvantage with the Morley antenna is that the transmitter requires a relatively greater power output for compensating for the mispointing of the transmitted signal.
Consequently, what is needed is a small single antenna that is suitable for residential use, can simultaneously communicate with a geostationary FSS satellite and with a plurality of geostationary DBS satellites, and minimizes the amount of transmitter output power for transmitting to the FSS satellite.
The present invention provides a small single antenna that is suitable for residential use, can simultaneously communicate with a geostationary FSS satellite and with a plurality of geostationary DBS satellites, and minimizes the amount of transmitter output power for transmitting to the FSS satellite.
The advantages of the present invention are provided by an antenna that includes a reflector having a first axis, a second axis, a focal zone that is about parallel to the first axis, and a focal point located within the focal zone. According to the invention, a transmit feed is located at or about at the focal point, and at least one receive feed is located at about the focal zone. Preferably, the reflector is an elliptically-shaped offset-type parabolic reflector, and the transmit feed is part of a bidirectional feed that includes an integral receive feed. The bidirectional feed transmits and receives an RF signal carrying digital information signals to and from a first satellite, such as an FSS satellite, and each respective receive feed receives a signal from satellite, such as a DBS satellite.
In a preferred embodiment, the present invention provides an antenna that includes an elliptically-shaped offset-type parabolic reflector having a first axis, a second axis, a focal direction, a focal zone that is about parallel to the first axis, and a focal point located within the focal zone. Accordingly, a transmit feed is located within the focal zone, and at least one receive feed located at about the focal zone. A support arm extends from the bottom of the reflector in the focal direction of the reflector and supports the transmit feed at the focal point and each receive feed within the focal zone.